The Gross Reason You Should Never Wear Shoes in Your House

“The surface of your flooring makes an enormous difference,” says Alessandra Leri, professor of chemistry and biology at the school and the lead author of the study. “If you have carpets, they function as a reservoir of bacteria.” But no matter the interior floor surface, she says, “shoe soles are a serious vector of transmission of fecal bacteria from the outdoor environment to the indoor environment.”

PFAS, the “forever chemicals” so named for how long they linger in the environment and our bodies, are regularly picked up by shoes and used in manufacturing the soles. Lead dust, which can often be stirred up and released into the air during remodeling of older homes and other buildings, can cling to shoes as well. Pesticides, used both on farms and in home gardens, are similarly free-riders on our shoes.

In most homes in which people do not remove their shoes upon entering, the area nearest the front door is generally the most contaminated. “We found that the first four steps at the entrance to the household are the germiest floor area in the home,” says Gerba. “We also did tracer studies putting dye and tracer viruses on the bottom of shoes and could see how they left a trail on the floor.”